This invention relates to a control system which dispenses fluid onto a substrate, and more particularly, to a controller which maintains relatively constant the amount of fluid per unit length dispensed onto a substrate during varying rates of relative movement between the dispenser and the substrate.
Devices for vending fluid from a dispenser onto a moving substrate are typically found in coatings and adhesive applications. For both coatings and adhesive applications the relative movement between the substrate and the dispenser varies while the rate at which the fluid is being dispensed remains constant. As a result, the fluid dispensed on the substrate may have uneven thickness.
In some cases there may be insufficient material such that the quality of the product is unacceptable. In other cases the material may be too thick, wasting material, and which may also have an adverse effect on quality. A device or system to closely regulate the dispensed fluid would be useful to reduce the amount of excess material dispensed and otherwise to improve or assure the quality of the produced end product.
To solve the above problem in the adhesives area, the Ingenieurburo Hamprecht Company has developed a timer containing a module which attempts to modify the flow rate of the dispensed adhesive in proportion to a conveyor line speed. This particular module would appear to count a number of pulses from a pulse generator positioned to convert the movement of a substrate conveyor into a pulse signal for a selected period of time and thereafter latch the pulse count and present it to a digital to analog converter. The converter effects a current in a control mechanism which regulates the flow rate of adhesive to a dispensing unit. The module also supplies a minimum control signal by adding current to the current established by the converter. One of the major drawbacks of this system is with the summation of totaling of current to provide a minimum flow rate signal. By adding current, the velocity at which maximum flow rate occurs is lessened because the current necessary to achieve maximum flow rate is reached sooner. To correct this condition such that maximum flow rate is not reached until desired, the time period selection member must be experimentally varied until the desired condition occurs. As can be seen, the desired condition is not selected by establishing a fixed time constant. Accordingly, inaccuracies will inevitably result from the inability to select and maintain a time constant in which maximum flow rate occurs at a desired velocity.